Having been in the fitness industry for as long as I have, a person becomes a trained observer at the human form and motion. Mistress often caught me staring at a people of both sexes, fit, unfit, tall, short, old and young and ask me what am I looking at. This is especially true with shapely women. While the vessel of a beautiful woman in revealing clothing on a summer day is visually appealing I was looking deeper and Mistress knew that.
Rather than comment on a specific body part, I would say, "She has upper cross syndrome.""She has an anterior pelvic tilt.""She has a knee/ankle/foot problem." It made for a great party trick, when I after an hour or two of watching people I could tell them all the problems I think they have and sure enough more often than not, it was a past problem or current problem.
Okay, I am not some Svengali here. What I do is as natural to me based on observation and training as it is the same for a cubicle worker who can scan a dozen graphs and see all the trends in the blink of an eye. I have put a tape measure around thousands of people, I have 10,000 hours of observing people from a scientific purpose and of course that is going to jump over to how I see John and Jane Sixpack walk around the mall. I would say that all great personal trainers or health motivators can do the same. Problem is most personal trainers are morons and couldn't create a great lifestyle program for a client on their own if they tried. Yes that is a dig, but so be it, truth hurts. Again I have a lot observation and personal experience here.
Next time you're walking down the street and you notice that someone has rolled shoulders or the hips look like they tip forward just a bit too much for normal, you're becoming a trained observer. The bikini she's wearing is just window dressing.